This invention relates to a process for stabilizing copolymers of ethylenically unsaturated fluoro compounds with vinyl ethers against gel formation, the stabilized copolymers being particularly useful as components of high quality coatings and finishes, especially for bridge ironwork and architectural maintenance and in automotive applications.
Copolymers of ethylenically unsaturated fluoro compounds, especially of fluoroolefins, with vinyl ethers as well as coating compositions containing such copolymers are well known, for example, from U.S. Pat. Nos. 3,306,879 (Pattison); 3,390,203 (Engelhardt); 3,429,845 (Bechtold et al.); 3,476,827 (Engelhardt); 3,762,940 (Bechtold); and 4,859,755 (Schlipf et al.), all of which are incorporated by reference herein.
In coating applications, the coating compositions frequently are applied from a solution in an organic solvent, so that good solubility of such compositions and stability of the solutions are important. Unfortunately, copolymers of ethylenically unsaturated fluoro compounds with vinyl ethers have a tendency to gel. Gelation can begin in the free radical-initiated copolymerization process itself or later, upon standing of a copolymer-containing composition or of isolated copolymer. Attempts have been made in the past to improve the stability of solutions of such copolymers by adding a tertiary organic amine or a tertiary organic phosphine to the solution, or by conducting the copolymerization in the presence of a 2,2,6,6-tetrasubstituted piperidine, as described in Japanese laid-open (Kokai) patent applications of Dainippon Ink & Chemicals, Inc., publication numbers 62-292813, 62-104814, and 62-292814, respectively. As another solution, Dainippon suggests the incorporation in the copolymer of a tertiary amine group-containing comonomer, as disclosed in Japanese laid-open application 2-140210.
Even when copolymers of ethylenically unsaturated fluoro compounds with vinyl ethers are used in aqueous dispersions, such as, for example, latices, the presence of gel is undesirable because such dispersions are nonuniform and difficult to apply and give uneven, poor quality coatings.
Addition of amines either to the copolymers or to the copolymerization reaction is said to be effective in preventing gelling. It seems that one of the purposes of the amine is to neutralize any acid that may be initially present or subsequently formed. This method of stabilizing the copolymers often has the shortcoming of imparting to the compositions an undesirable yellow color. Further, lower boiling organic amines sooner or later evaporate from the compositions, so that their stabilizing effect is lost.
It is, therefore, desirable to provide a process for stabilizing copolymers of ethylenically unsaturated fluoro compounds with vinyl ethers which would not have the above shortcomings.